1. Field of the Invention
This invention relates to clipper seams for use in joining the ends of a papermakers belt or the like.
2. Description of the Prior Art
In papermaking machines, a papermakers belt in the form of an endless belt-like structure is supported on and advanced by various machine rolls during the papermaking process. Papermakers belts carry various names depending on their intended use. By way of example, papermakers belts include forming fabrics, wet press felts, and dryer felts and fabrics, to name just a few. In each case, the belt or fabric is joined at its ends to form an endless belt which is supported and controlled by various machine rolls associated with the papermaking machine.
The prior art employs various types of seams which are joined together through the use of a pintle in order to facilitate insertion and removal of the papermakers belt from the papermaking machine. A very common type of seam is one employing metal clipper hooks arranged in an alternating relationship on either end of a papermakers belt to receive a pintle to join the ends of the belt together. The clipper hooks may be inbedded directly into the ends of the belt, or may be secured to seam webbings which are in turn attached or secured to the ends of the belt through suitable stitching.
Other types of arrangements for joining the ends of a papermakers belt include those in which the metal hooks are replaced by pintle receiving loops that are made from a synthetic material and are usually integral with the yarns used to define either the ends of the papermakers belt or the seams attached to the belt.
Certain problems exist with each of the prior structures used to secure the ends of the various belts together. In some papermakers belts, the ends of the belt are joined in an abutting relationship and held that way through the use of clipper hooks inserted in a webbing, the whole of which is attached to the underside of the belt. Since the tension line of the seam is below that of the fabric, the seam tends to move upwards so that both tension lines become coplanar. This in turn causes the abutting ends of the papermakers belt to press up against the paper sheet. When the paper sheet lies between a machine roll and the felt seam, the pressure between roll and seam increases thereby causing seam marking in the sheet, especially in the case of fine or critical grades of paper. Another problem associated with this type of seam occurs when the seam either makes or leaves the contact of a machine roll. A bouncing of the papermakers belt occurs, which leads to further marking of the paper sheet, paper sheet breaks and a rapid weakening of the fabric structure in the seam area.
Thread unraveling is a problem which occurs in papermakers belts in which the cut ends of the belt are exposed to either, or both, the paper sheet being formed, or the machine rolls. The last several threads in the cross machine direction at the end of a papermakers belt have the potential to become loose, a condition which may lead to further marking of the paper sheet.
Typically, in the case of a clipper seam that is attached to a papermakers belt, the sewing threads used to secure the seam to the ends of the belt are proud due to the typically hard and unyielding belt surface. Since the sewing threads are exposed on the surface of the belt and the surface of the seam, the threads are prone to wear, which ultimately leads to seam failure. The proud sewing threads can also cause paper marking problems.
One problem associated with the type of clipper seam that employs clipper hooks imbedded into the ends of the belt is that the hooks are normally proud on both the paper side and machine-roll side of the belt. This may lead to sheet marking on the paper side and to wear problems on the machine-roll side. Another problem is that the last few threads of the seam must be sealed or else the hooks will not imbed properly.
There is thus a need for a clipper seam for joining the ends of a papermakers belt in which the chances of seam failure are substantially reduced, the problem of unraveling is eliminated, and the problem of paper marking is severely curtailed. The present invention is directed toward filling that need.